I think this has already been discussed and the consensus was that it would be unnecessary (?)
If you really want this i'm pretty sure you can inject it into your webpage with JS and a simple script pretty easily.
As per Tryninja:
theymos (or some famous members) already said somewhere that this would make the forum have the "too much price dependent" vision.
1 BTC = 1 BTC. And that's what matters.
I'm not sure what his source for this is, couldn't find it.